Tentative fix for Issue #351

The fix entails a modification to wait_for_vrf_del_ready()

In both the legitimate case (user trying to delete a VRF after having removed all network attachments) `lanAttachState` very briefly transitions to DEPLOY before transitioning to its final state of NA.  However, in this case, `isLanAttached` (in the same data structure) is False.  Whereas in the illegitimate case (user hasn't removed network attachments) `isLanAttached` is True.  Hence, we can leverage `isLanAttached` to differentiate between legitimate and illegitimate cases.

Adding another conditional that checks if `lanAttachState` == DEPLOY AND `isLanAttached` == True.  If this is the case, then the user is trying to delete a VRF that still contains network attachments and we now fail immediately with an appropriate error message.

Other changes:

1. Add standard python logging

2. Use `ControllerVersion()` to retrieve the NDFC version and remove import for `dcnm_version_supported`

3. Use `FabricDetails()` to retrieve fabric type.

4. Modify `update_attach_params()` to improve readability by first populating the neighbor dictionary before appending it.  This way, we avoid a lot of unsightly accesses to element 0 of the list.  For example:

```python
                    if a_l["peer_vrf"]:
                        vrflite_con["VRF_LITE_CONN"][0]["PEER_VRF_NAME"] = a_l["peer_vrf"]
                    else:
                        vrflite_con["VRF_LITE_CONN"][0]["PEER_VRF_NAME"] = ""
```

Becomes:

```python
                    if a_l["peer_vrf"]:
                        nbr_dict["PEER_VRF_NAME"] = a_l["peer_vrf"]
                    else:
                        nbr_dict["PEER_VRF_NAME"] = ""
```

5. diff_for_attach_deploy() - Reduce indentation by reversing logic of conditional.

The following:

```python
                                    if wlite["IF_NAME"] == hlite["IF_NAME"]:
                                        # Lots of indented code ...
```

Becomes:

```python
                                    if wlite["IF_NAME"] != hlite["IF_NAME"]:
                                        continue
                                    # unindent the above code
```

6. get_have()

- Reduce indentation levels by reversing logic (similar to #5 above)

7. Add method want_and_have_vrf_template_configs_differ(), see next item.

8. diff_for_create()

- Leverage want_and_have_vrf_template_configs_differ() to simplify.

9. Add method to_bool(), see next item

10. diff_for_attach_deploy()

- Simplify/shorten by leveraging to_bool()

11. In multiple places, ensure that a key exists before accessing it or deleting it.

12. Run though black

13. Several minor formatting changes for improved readability.

Author: allenrobel